X-ray is widely applicable in the field of industrial nondestructive detection, security inspection and the like. For a large-sized subject to be detected, such as a boiler, a airspace engine, a bulk cargo at the airport/railway/custom, a car load freight in a car/truck/container/train or the like, the high-energy X-ray is required for the fluoroscopic inspection, which is usually generated by using an electron accelerator with energy above 2 MeV. A basic method for generating X-ray by the electron accelerator comprises: generating an electron beam using an electronic gun, accelerating the electron beam to obtain high energy using an electric field, and generating X-ray by using the high-energy electron beam to bombard a target. The high-energy X-ray fluoroscopic imaging system makes use of the high penetration capability of X-ray. When X-ray penetrates an object to be inspected (a subject), the intensity of X-ray weakens, and the extent of weakening is related to the density, the shape, the thickness, the material of the subject and etc. The intensity information of the X-ray after passing through the subject is acquired by using a detector, and then a fluoroscopic image reflecting the information of the subject such as the shape, the structure, even the material and the like is obtained through e.g. signal processing, algorithm analysis, image reconstruction and the like. Thus, the purposes, such as structure analysis, defect detection, cargo check, hazardous article recognition, contraband inspection and the like can be realized.
The inspection system for large-sized cargoes is divided into two types, one type using high-energy X-ray source, and the other type using isotope radioactive source. The system using high-energy X-ray source generally uses an electron accelerator having energy above 2 MeV to generate X-ray by bombarding a target. At present, NUCTECH Company Ltd. is one of the leaders in this technology application all over the world, and owns a large amount of patents and mature products. The system using isotope radioactive source generally uses γ-ray generated by the radioactive isotope Cobalt-60 (Co-60) as ray source, and the energy of γ-ray are 1.17 MeV and 1.33 MeV respectively. With respect to the inspection system for large-sized cargoes using Cobalt-60, on one hand, the energy of rays is low, the penetration energy is limited, and the volume of the subject that can be checked is limited; on the other hand, Cobalt-60 has a inherent half-time period of 5.27 years, and thus the ray source has to be replaced after a period of time, otherwise the image quality will degrade due to the weakening of ray intensity. The inspection system for large-sized cargoes using Cobalt-60 has many problems in safety management due to the inherent radioactivity of Cobalt-60, unlike the electron accelerator system, in which X-ray is generated only when power is on and the beam is produced, and which is safe when the beam is stopped or power is off. Therefore, more than 90% of the current large cargo inspection systems make use of high-energy X-ray source.
In prior art, all usages of high-energy X-ray are to obtain an X-ray beam in front of the electron beam which is bombarding the target to perform fluoroscopic imaging application, and make use of the portion of the X-ray having the highest energy and the largest intensity as far as possible. Generally only one X-ray beam is extracted for the system with only one inspection channel, and thus the inspection speed is slow and the efficiency is low.
The Chinese patent, “a dual-channel assembled mobile container or vehicle inspection system (Patent No.: CN2840027Y)”, discloses a system in which the γ-ray generated by Cobalt-60 is used as ray source and two gate-type structural inspection channels on the left and right sides respectively are constituted by two L-shaped detectors, so that “the passing rate of detection is improved by 2-4 times” can be realized. The Cobalt-60 γ-ray source has its particularity in using and processing, such as a shutter device and the like, and has shortages such as low energy, limited penetration capability; short inherent decay, short life, which requires periodic replacement; long-term radiation, large difficulty in safety management, etc.
In view of the disadvantages in the prior art, the present invention provides a system in which an electron accelerator is used as ray source and at least two X-ray beams are respectively obtained by at least two collimators, to simultaneously perform fluoroscopic imaging on the subjects in at least two channels. In particular, the present invention also provides a system in which a high-energy electron accelerator is used as ray source and two X-ray beams are respectively obtained by collimators in two lateral positions, to simultaneously perform fluoroscopic imaging on the subjects in two channels. Compared with the prior art, the system has advantages such as low cost, high speed, multi functions, high image quality and high safety, etc.